The present invention relates to an electronic timepiece (clock and watch) incorporating an electric power generator for generating electric energy by utilizing externally available energy, and storage means for storing the electric energy generated by the electric power generator, and capable of performing a time-keeping operation by use of the electric energy generated or the electric energy stored, and a method of controlling the same.
There have lately become commercially available and been put to practical applications various types of electronic timepieces incorporating an electric power generator for converting external energy such as optical energy, mechanical energy and so forth into electric energy, and capable of driving timing means by utilizing the electric energy.
Among the electronic timepieces incorporating such an electric power generator, there are included a solar cell electronic timepiece using a solar cell for the electric power generator, a mechanical power generation type electronic timepiece for utilizing electric energy converted from mechanical energy generated by rotation of a rotary weight, a temperature difference electric power generation timepiece for generating electric power by utilizing difference in temperature between the opposite ends of a plurality of thermocouples connected in series and so forth.
The electronic timepieces incorporating any of these electric power generators have storage means as well which is incorporated therein for storing electric energy generated by an electric power generator thereof by use of the external energy when die external energy is available so as to enable the electronic timepieces to be driven continuously and stably all the time even after the external energy is gone.
Such electronic timepieces as described above come to stop performing a time-keeping operation without supply of the external energy and upon completing discharge of the electric energy stored in the storage means. However, at least after the restart of the supply of the external energy, these electronic timepieces resume the time-keeping operation.
Among the electronic timepieces incorporating various types of electric power generators as described above, a solar cell timepiece is disclosed in, for example, JP, H4-50550, B.
A power supply system of such a conventional electronic timepiece is described hereinafter with reference to FIGS. 6 and 7. FIG. 6 is a circuit diagram showing the configuration of the conventional electronic timepiece, and FIG. 7 is a circuit diagram showing the circuit configuration of a common transmission gate.
With the electronic timepiece shown in FIG. 6, electric power generator 1 is connected with storage means 3 and timing means 2 via charge/discharge control means 4.
The electric power generator 1, which is a solar cell, a diode 43, and the timing means 2 form a closed circuit. The timing means 2 is comprised of a timing block 5 for executing a time display operation by use of electric energy, and a capacitor 23 having a capacitance on the order of 10 xcexcF, which are connected with each other in parallel.
Further, the electric power generator 1, a diode 44, second switching means 42, and the storage means 3 form another closed circuit The second switching means 42 is for use in charging the storage means 3, but description thereof is omitted herein.
A transmission gate 60, which is first switch means 41, interconnects the negative terminal of the capacitor 23 and that of the storage means 3 such that the capacitor 23 and the storage means 3 are connected in parallel.
In order to enable the timing means 2 to restart its operation by connecting the electric power generator 1 with only the timing means 2 when power generation by the electric power generator 1 is restarted after complete discharge of electric energy from the storage means 3, the transmission gate 60 is made up to be controlled so as to be in the OFF condition at the time of reactivation.
Similarly, the second switching means 42 is also made up to be controlled so as to be In the OFF condition at the time of the reactivation of the timing means 2.
That is, the operation of the timing means 2 remains suspended when the electric power generator 1 is not generating power while the storage means 3 has been discharged substantially to its fully depleted state, however, upon the restart of power generation by the electric power generator 1, electric energy generated is delivered only to the timing means 2.
However, as shown in FIG. 7, the transmission gate 60 normally has a configuration of two transistors connected in parallel, that is, the configuration wherein the source terminal (S) and the drain terminal (D) of a transistor 61, and those of a transistor 62 have connections in common, respectively. In this case, for both the transistors 61, 62, a MOS field effect transistor (hereinafter referred to as xe2x80x9cMOSFETxe2x80x9d) is used.
Further, in a normal configuration, a P-channel MOSFET is used for the transistor 61 and an N-channel MOSFET is used for the transistor 62.
Because controlling of on/off of the transistor 61 as well as the transistor 62 requires an inverting signal respectively, there is a need for providing an internal inverter 63.
The internal inverter 63, and the transistors 61, 62 come into operation by a switching control signal S4 outputted from the timing block 5 inside the timing means 2. The switching control signal S4 is a signal which will be at the level of a potential of the negative terminal VSS1 of the timing means 2 when a voltage between the terminals of the capacitor 23 is at a predetermined value or higher, and will be at the ground potential level when the voltage is lower than the predetermined value.
For turning off the transmission gate 60, it is necessary to render a potential of the gate terminal of the transistor 62 identical to that of the source terminal thereof, and further, to render a potential of the gate terminal of the transistor 61 identical to the ground potential by the agency of the internal inverter 63. However, even if such control as described can be effected, the transistors 61, 62 have a PN junction formed therein respectively, and particularly, in the transistor 62, there is formed a diode wherein current flows in the direction of the arrow Q from the source terminal (S) to the drain terminal (D).
Accordingly, the transistor 62 has a circuit configuration wherein even if the transistor 62 is in the off condition, its circuit is not completely cut off so that electric energy stored in the storage means 3 is dischargeable towards the timing means 2 all the time.
Thereupon, an oscillation circuit, and other control circuits within the timing block 5 of the timing means 2 are not completely turned off, and wasteful leakage current continues to flow for many hours, thereby resulting in progress in the discharge from the storage means 3.
As a result, there have arisen problems in that, once the electronic timepiece described in the foregoing is kept out of use for many hours, even if power generation is rested, time ranging from several tens of minutes to several hours from the restart of power generation is required for recharging up to a level enabling the tiring means 2 to continue its operation, and if power generation by the electric power generator 1 comes to a stop during a period of the recharging, the timing means 2 stops its operation immediately,
In other words, even if power generation is restarted by the electric power generator 1, electric energy generated by the electric power generator 1 is used simply for charging the storage means 3 during a period of recharging the storage means 3 to replenish a portion of the electric energy stored in the storage means 3 over-discharged due to leakage current as described above, thereby preventing the electric energy generated to be directly utilized as energy used for performing the time-keeping operation by the timing means 2, Consequently, the restart of the time-keeping operation is delayed, posing a major problem with the initial startup operation characteristics of the electronic timepiece incorporating the electric power generator.
The invention has been developed to overcome the above-described problems, and it is therefore an object of the invention to provide an electronic timepiece incorporating an electric power generator, wherein occurrence of over-discharge from storage means, more than inevitable, is prevented even wit the elapse of many hours after suspension of power generation by the electric power generator, so that the time-keeping operation can be started immediately upon the restart of power generation by the electric power generator.
To this end, the invention provides an electronic timepiece having the following configuration, and a method of controlling the same.
The electronic timepiece according to the invention comprises an electric power generator for converting external energy into electric energy, a storage means for storing tie electric energy generated by the electric power generator, a timing means for performing a time-keeping operation by use of the electric energy supplied from the storage means or the electric power generator, and a charge/discharge control means for executing transfer or shutoff of the electric energy among the electric power generator, the storage means, and the timing means, wherein a voltage measurement means for measuring a voltage between the terminals of the storage means is included, and the charge/discharge control moans is provided with a means for completely shutting off a discharge path of the storage means when an amount of the actual capacity that remains in the storage means is less than a predetermined amount according to the voltage between the terminals of the storage means as measured by the voltage measurement means.
The electronic timepiece wit these features preferably further comprises a timing stoppage detection means for detecting stoppage of the time-keeping operation in the timing means, and a means for maintaining a condition in which the discharge path is completely shut off by the agency of the charge/discharge control means by nullifying either a voltage measuring operation or measurement results of the voltage measurement means during a period from the complete shutoff of the discharge path of the storage means by the charge/discharge control means to a time when the stoppage of the time-keeping operation in the timing means is detected by the timing stoppage detection means,
The invention also provides the method of controlling the electronic timepiece as described above, wherein the electronic timepiece is controlled such that an amount of the actual capacity that remains in the storage means does not go far below a predetermined amount by completely shutting off a discharge path of the storage means at least when the amount of the actual capacity that remains in the storage means is less than the predetermined amount.
In the method of controlling the electronic timepiece with these features, information on the amount of the actual capacity that remains in the storage means may be obtained by measuring the voltage between the terminals of the storage means,
In the method of controlling the electronic timepiece with all those features, during a period from the complete cutoff of the discharge path of the storage means to at least a time when the time-keeping operation by the timing means is once stopped, a completely shut off condition of the discharge path is preferably maintained regardless of measurement results on the voltage between the terminals of the storage means.
Furthermore, when the amount of the actual capacity that remains in the storage means is less than the predetermined amount and the electric energy generated by the electric power generator exceeds a predetermined amount, the electronic timepiece is preferably controlled such that the electric energy generated by the electric power generator is preferentially delivered to the timing means.
Or when the amount of the actual capacity that remains in the storage means is less than the predetermined amount and the electric energy generated by the electric power generator exceeds the predetermined amount, the electronic timepiece may be controlled such that the electric energy generated by the electric power generator is delivered to the timing means and the storage means.
Hence, according to the invention, it is possible to prevent the occurrence of over-discharge of the storage means, which used to pose a problem in the past, so that the restart of the electronic timepiece can be effected with certainty even after the operation of the electronic timepiece is interrupted, and in addition, once the electronic timepiece restarts its operation, all portions of electric energy with which the storage means are charged by then can be utilized for the time-keeping operation even if power generation comes to a stop thereafter. Thus, the electronic timepiece capable of performing stable operation can be implemented.